This invention relates generally to a brake clearance adjuster for a vehicle such as a work machine, off-highway truck, or the like, and more particularly, to a brake clearance adjuster for automatically maintaining a predetermined maximum brake clearance regardless of the wear condition of the brake.
Currently, a wide variety of devices for adjusting the clearance or slack between rotors and frictional elements of brake mechanisms are well known. Reference, for instance, Kovac U.S. Pat. No. 2,568,858, issued Sep. 25, 1951; Frayer et al. U.S. Pat. No. 2,900,052 issued Aug. 18, 1959 to the Goodyear Tire and Rubber Company; Crossman U.S. Pat. No. 3,554,336 issued Jan. 12, 1971 to the Goodyear Tire and Rubber Company; Cunningham U.S. Pat. No. 3,517,785 issued Jun. 30, 1970 to the Bendix Corporation; Kimata U.S. Pat. No. 3,575,268 issued Apr. 20, 1971 to Isuzu Motors Limited; Davidson U.S. Pat. No. 4,478,316 issued Oct. 23, 1984; Nowosielski U.S. Pat. No. 5,497,859 issued Mar. 12, 1996; and Naedler et al. U.S. Pat. No. 5,607,033 issued Mar. 4, 1997 to Mark+2 Technologies, Inc.
However, the known clearance adjuster devices suffer from various shortcomings and limitations, for instance, complexity and cost disadvantages. In particular, numerous of the known devices are located within the piston element of the brake mechanism so as to add substantial complexity and cost to the piston element. This also makes access to the adjuster mechanism difficult for performing maintenance and service. Additionally, several of the known adjuster devices bear or transmit at least a portion of the braking force, increasing the design requirements thereof. Further, several of the known devices only allow relatively large increments of advancement of the piston element as the frictional elements of the brake wear compared to the amount of clearance or slack provided, such that the maximum allowed slack is substantially greater when the brakes are worn compared to when new.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
According to one aspect of the invention, an automatic clearance adjuster mechanism which maintains a predetermined maximum brake clearance for a brake for retarding rotation of a rotatable member about a longitudinal axis is disclosed. The brake includes a brake housing having a fluid receiving chamber and a piston element disposed partially within the fluid receiving chamber. The piston element is movable by pressurized fluid in the chamber longitudinally in a first or extend direction outwardly with respect to the fluid receiving chamber for applying a pressure for retarding the rotation of the rotatable member, and in an opposite retract direction to provide clearance for freer rotation of the rotatable member. The brake also includes a longitudinally extending rod mounted to the brake housing external to the piston element. The present automatic clearance adjuster mechanism includes a sleeve element disposed about the rod, and a biasing element disposed for releasably holding the sleeve element against the rod for preventing movement thereof along the rod to limit the retraction of the piston element to a predetermined distance relative to the sleeve element. The present mechanism also includes a release element disposed to release the biasing element when the piston element is moved in the first or extend direction to allow the sleeve element to be moved by the piston element to an advanced position along the rod and allow the biasing element to hold the sleeve element against the rod in the advanced position when the movement in the extend direction is stopped or the piston element is moved in the opposite direction, the sleeve element when held against the rod in the advanced position limiting the retraction of the piston element to a predetermined distance relative to the advanced position.
According to a preferred aspect of the invention, the sleeve element includes a split sleeve, the biasing element includes at least one retainer ring disposed around the split sleeve, and the release element comprises cooperatively engageable serrated portions on the split sleeve and on the rod which allow movement of the split sleeve along the rod in the first or extend direction.
According to another preferred aspect of the present invention, the sleeve element includes a split sleeve having a longitudinally tapered outer surface, and the biasing element includes a bushing disposed around the split sleeve and having a longitudinally tapered inner surface positioned for slidable engagement with the tapered outer surface for compressing the split sleeve to hold the split sleeve around the rod when the piston element is retracted, and a compression spring disposed for retracting the piston element and urging the tapered surfaces into the slidable engagement.